Compact Dual-band Filters Using Substrate Integrated Coaxial and Slot-line Resonators

This paper reports on the EM design and practical validation of a hybrid implementation scheme for split-type dual-band bandpass filters (BPFs) using a low-cost substrate integrated PCB approach. Size compactness is achieved by combining substrate integrated coaxial cavity resonators (SICRs) and slot-line resonators (SLRs) within a dual-band filtering cell (DBFC). Band selectivity can be increased by cascading multiple first order DBFCs. A broad spurious free out-of-band response can be achieved by altering the orientation of the DBFCs and the RF ports. The operating principles of the dual-band SICR-SLR filtering concept are demonstrated through synthesized examples and EM analysis. For proof-of-concept validation purposes first-order and third-order dual-band BPFs were designed, manufactured, and measured at C band.